Inorganic arsenic: A non-genotoxic carcinogen

Area of Science:

• Environmental Toxicology
• Carcinogenesis

Background:

• Inorganic arsenic exposure is linked to various toxicities, including cancer.
• The mechanism involves metabolic activation to trivalent arsenicals that interact with cellular proteins.

Purpose of the Study:

• To elucidate the mode of action for inorganic arsenic-induced toxicities and cancer.
• To evaluate the genotoxicity and dose-response relationship of inorganic arsenic.

Main Methods:

• Review of in vitro, in vivo, and human epidemiological studies on arsenic toxicity and genotoxicity.
• Analysis of cellular responses, including protein binding, cell death, and regenerative proliferation.
• Assessment of genotoxicity markers and confounding factors in human studies.

Main Results:

• Arsenic's toxicity stems from trivalent arsenicals reacting with sulfhydryl groups in proteins, leading to cell death and proliferation.
• Arsenicals do not directly interact with DNA; observed genotoxicity markers are likely due to cytotoxicity.
• Human studies show difficulties in interpreting genotoxicity data due to exposure assessment and confounding factors.
• A non-linear dose-response relationship with a threshold for biological effects, including cancer, was observed.

Conclusions:

• Inorganic arsenic induces toxicity and cancer risk via indirect mechanisms involving protein damage.
• Genotoxicity findings in humans are often confounded by cytotoxicity and other factors.
• A threshold exists for inorganic arsenic's biological effects, suggesting non-linear dose-response relationships are critical for risk assessment.